JP4871339B2 - Sputtering method - Google Patents

Description

  The present invention relates to a sputtering method in a multi-cathode ionization physical vapor deposition apparatus, and in particular, plasma assisted sputtering in which two or more cathodes are arranged in the same reaction vessel and used to perform deposition by sputtering. A film deposition device in which sputtered atoms from the target are ionized in the plasma region and accelerated by the self-bias voltage onto the surface of the wafer and onto the surface of the wafer having holes or trenches in the submicron size. accumulate.

  Magnetron sputtering equipment is widely applied to deposit thin films on substrates or wafers used in the semiconductor industry. In depositing a film on a wafer, such as a silicon wafer, one of the primary conditions is film uniformity. Multi-cathode sputtering devices have been invented and used to deposit films with higher uniformity. However, this apparatus has severe problems when depositing a film on a patterned wafer, for example on a surface having deep holes or grooves of micron size. This problem will be described in detail with reference to FIGS.

  FIG. 8 shows a longitudinal cross-sectional view of a conventional multi-cathode sputtering apparatus, while FIG. 9 shows a view from above of an upper wall with several cathodes arranged in a predetermined arrangement. A reaction vessel 100 used as a wafer processing chamber includes multi-cathodes 101a to 101d, a wafer holder 102, a gas introduction unit 103, and a gas discharge unit 104. In FIG. 8, for example, the number of cathodes is four, and these four cathodes 101a, 101b, 101c and 101d are provided in an inclined state. Each of the cathodes 101a to 101d is made of a metal such as Al, Ti, or Ta. These cathodes are sputtered to deposit a film on the wafer 112 mounted on the wafer holder 102. The cathodes 101 a to 101 d are electrically insulated from the reaction vessel 100 using the dielectric material 105. In general, a plurality of magnets 106 having a particular arrangement are arranged on the upper surface of each cathode. Further, the magnets 106 provided on the respective cathodes are rotated around an axis displaced from the center of the associated cathode 101 or a central axis by a rotation mechanism (not shown). Each cathode 101 is connected to a DC power source (not shown).

  The wafer holder includes a metal electrode 108, a dielectric material 109, a side wall 110, and a shaft 111. The wafer 112 is horizontally disposed on the metal electrode 108 as shown in FIG. The shaft 111 is connected to an electric motor (not shown), thereby rotating the wafer holder 102 about its central axis 102a.

  Plasma is created inside the reaction vessel 100 by applying power to one or several cathodes 101a-101d while maintaining the internal pressure of the reaction vessel 100 at an appropriate pressure. Due to the higher negative voltage of the cathodes 101a-101d, ions in the plasma are accelerated and sputtered toward the cathode. These sputtered atoms then travel through the plasma and deposit on the wafer 112 and other surface areas that the plasma does not contact.

  The flow of sputtered atoms coming from each of the inclined cathodes 101 a to 101 d toward the horizontal wafer 112 is not uniform in the radial direction on the surface of the wafer 112. A virtual flow of sputtered atoms from the cathode 101a is indicated by an arrow 113 in FIG. In order to obtain a uniform thin film on the surface of the wafer, the wafer holder 102 is rotated about its central axis as described above. This results in a uniform film.

Sputtered atoms from the cathode are in a neutral state. Because very low pressures are used for sputtering, for example, less than 10 mTorr (1.3 Pa), the sputtered atoms are subject to a few collisions in the gas phase before being deposited on the wafer surface. Become. Even though there are Ar ⁺ and Ar ^* excited state atoms that can ionize the sputtered atoms by collision in the plasma, it appears that sputtered atoms are less likely to be ionized by a smaller number of gas phase collisions. Thus, most of the deposition on the wafer surface is caused by neutral atoms.

  Film deposition with neutral atoms is useful when the film is deposited on a planar surface. However, when there are holes or trenches (trench), especially when there is such a sub-micron size, film deposition by neutral atoms will be limited. This will be described with reference to FIGS. Since sputtered atoms arrive at an angle with respect to the surface of the wafer, most of the film 114 deposited inside the holes or trenches 115 is a wall facing the flow of atoms, as shown schematically in FIG. Get up in the part. This results in asymmetric film deposition on the sidewalls of the holes or grooves 115 as shown in FIG. Further, if the hole diameter or groove width is sub-micron in size and has a higher aspect ratio, the membrane becomes progressively thinner toward the bottom of the hole or groove 115. This is because only a few atoms reach the bottom of the hole or groove 115. This causes the film on the sidewall of the hole or groove to be discontinuous. Therefore, application of the above-described sputtering apparatus to a wafer having a pattern is limited.

  Patent Document 1 below discloses an example of a multi-cathode sputter wafer processing chamber. The multi-cathode sputter wafer processing chamber has four cathodes that are inclined at the ceiling. The required magnetic multilayer film is deposited on a wafer mounted on a wafer holder by appropriately sputtering each of the four cathodes.

JP 2002-167661 A

  An object of the present invention is to deposit a generally uniform film on the inner surface of holes or grooves created in the wafer surface using neutral atoms generated at the tilted cathode or target by sputtering. In addition, when the wafer has patterned deep holes or grooves with higher aspect ratio, it has good coverage from the entrance to the bottom of the opening by using sputtered neutral atoms It is to deposit a film.

  It is an object of the present invention to provide a sputtering method that can form better sidewall and bottom coverage with patterned holes or grooves on the wafer surface by using neutral atoms sputtered on each of the inclined multi-cathodes. It is in.

Scan sputtering method of the present invention, be controlled to be the reaction vessel pressure to a pressure higher than 5 Pa,
Placing the wafer in a wafer holder in the reaction vessel and rotating the wafer;
With respect to the wafer, it is arranged to tilt the motor Getto and cathode,
Applying an rf current to the cathode from an rf generator ;
Ionizing sputtered atoms emitted from the cathode , generating plasma in the reaction vessel , and
The lower electrode provided in the wafer holder is ungrounded , non-RF connected, and non-DC connected so that the wafer is in a floating state in terms of potential.
When the plasma is generated by capacitive coupling of the rf power of the rf generator, a negative self-bias voltage is generated on the selected cathode to ionize sputtered atoms emitted from the cathode and negative bias Depositing a film on the inner surface of a hole or groove made in the wafer surface, so as to be accelerated by an electric potential ;
It is characterized by.

In the sputtering method, preferably, the cathode, in addition to the rf current includes a DC current is further supplied.

In the above sputtering method, preferably, the target is made of a high-k dielectric material, and the high-k dielectric material includes HfSiON.

  In order to achieve the above object, a multi-cathode sputter ionization physical vapor deposition apparatus according to the present invention is configured as follows.

  The first multi-cathode ionization physical vapor deposition apparatus is configured as follows. A wafer holder is provided on the bottom wall so as to rotate about its central axis, and at least two inclined cathodes are provided on the top wall for a wafer disposed on the wafer holder. Each of the cathodes is provided with a pressure control mechanism including a gas introduction unit and a gas discharge unit. Each of the cathodes is supplied with an rf current from an rf generator through a matching circuit. In the above apparatus, the internal pressure of the reaction vessel is controlled to be a relatively high pressure by a pressure control mechanism.

  According to the above apparatus, the plasma in the reaction vessel is generated under a pressure higher than 5 Pa (Pascal). This condition ionizes sputtered atoms, and film formation occurs mainly by accelerated ions on the wafer surface.

  In the above-described multi-cathode ionization physical vapor deposition apparatus, the apparatus preferably includes a central cathode parallel to the wafer at the center of the upper wall.

  In the above-described multi-cathode ionization physical vapor deposition apparatus, the apparatus preferably includes a DC source that supplies a DC voltage to the cathode.

  In the multi-cathode ionized physical vapor deposition apparatus described above, preferably one or more of the cathodes is supplied with a DC current in addition to the rf current.

  The second multi-cathode ionization physical vapor deposition apparatus is configured as follows. A wafer holder provided on the bottom wall for rotation about its central axis, and comprising a reaction vessel provided on the top wall with at least two inclined cathodes relative to the wafer mounted on the wafer holder; Each is adapted to be supplied with a DC voltage from a DC source, includes a pressure control mechanism including a gas inlet and a gas outlet, and a central cathode parallel to the wafer at the center of the upper wall. In the above apparatus, the internal pressure of the reaction vessel is controlled to be a relatively low pressure by a pressure control mechanism.

In the above apparatus, any one target material of the cathode is preferably a material having a high dielectric constant such as HfO ₂ or HfSiON.

Further in the above apparatus, dielectric materials or metals such as HfO ₂ , Si ₃ N ₄ , Al ₂ O ₃ and Hf, which form other dielectric materials on the wafer during co-sputtering. In which two or more cathodes are simultaneously supplied with rf or DC voltage.

  Each cathode has a magnet array for generating magnetic flux lines (magnetic flux) on its outer surface, and the magnetic flux lines penetrate the cathode surface and reach the inside of the reaction vessel.

  According to the present invention, films can be deposited on wafers with patterned holes or grooves having higher aspect ratios with better sidewall coverage and bottom coverage.

  Hereinafter, preferred embodiments will be described with reference to the accompanying drawings. Through the description of the embodiments, the details of the present invention will be clarified.

[Embodiment 1]
A first embodiment of the present invention will be described with reference to FIGS. A longitudinal sectional view of the multi-cathode sputter deposition reaction vessel 10 is shown in FIG. A bottom view of the multi-cathode arrangement is shown in FIG. The reaction vessel 10 is formed by a side wall 10a, an upper wall 10b, and a bottom wall 10c, and has a confidential structure. Further, the reaction vessel 10 includes two or several cathodes (for example, four cathodes 11a, 11b, 11c, and 11d) used as a target, a wafer holder 12, and a lower electrode that is a part incorporated in the wafer holder 12. 15 and insulating materials 13 and 14 for electrically insulating the cathode and the lower electrode 15 from other parts of the reaction vessel 10. The number of cathodes is preferably four. The four cathodes 11 a to 11 d are fixed to the inner surface of the upper wall of the reaction vessel 10 with an insulating material 13 in an inclined state. The four cathodes 11a to 11d are arranged at equal intervals along the circular outer edge of the upper wall.

  Inside the reaction vessel 10, there are a plurality of gas introduction portions 16 and gas discharge portions 17 for introducing a single gas or a mixture gas into the reaction vessel 10. The gas introduction part 16 is connected to a gas supply device (not shown), and the gas discharge part 17 is connected to a vacuum pump (not shown). Thus, the reaction vessel 10 has a pressure control mechanism including the gas introduction part 16 and the gas discharge part 17, which is for controlling the internal pressure to a desired pressure.

  The four cathodes 11 a to 11 d are provided with an inclination in the central portion of the upper wall 10 b parallel to the lower electrode 15. The cathode diameter is not critical and is selected according to other dimensions of the reaction vessel 10. For example, if the reaction vessel 10 is designed to process a wafer having a diameter of 300 mm, the diameter of the cathodes 11a to 11d is in the range of 200 to 400 mm.

The material of the cathode or the material of the target is usually a metal such as Al, Ti, Ta, Mn. Furthermore, even semiconductor or dielectric materials can be used as targets. Target made of a dielectric material, for example, SiO _2, SiN, a high-k dielectric materials such as HfON or HfSiON. All cathodes 11a-11d are made of the same material or made of different materials.

  Any magnet arrangement may or may not be provided on the outer surface of each of the cathodes 11a to 11d. In FIG. 1, a plurality of separate magnets 18 provided on the outer surface of each cathode are shown. Typically, these magnet arrays are rotated about an offset axis at the cathode or about the central axis. There is no special arrangement for the magnet 18. The configuration of the magnet array can be selected by considering the efficiency of target utilization and film uniformity.

  Each cathode (11 a to 11 d) is connected to the rf generator 19 through the matching circuit 20. The frequency of the rf generator 19 is not critical and is in the range of 10-300 MHz. Further, all of the cathodes 11a-11d may provide rf currents that operate at the same frequency or at different frequencies.

  Wafer holder 12 is provided on the bottom wall of reaction vessel 10 and is located at a distance of at least 50 mm below the nearest cathode. The wafer holder 12 is fixed to a shaft 21, and the shaft 21 is rotated by using an electric motor (not shown). The lower electrode 15 is usually made of a metal such as Al, and is connected to the rf generator 22 via the matching circuit 23. However, the application of rf power from the rf generator 22 to the lower electrode 15 is not essential for the purposes of the present invention. If rf current is applied to the lower electrode 15, the frequency of the rf current is not critical and is in the range of 100 KHz to 50 MHz. The wafer 24 on which the film is deposited is mounted on the lower electrode 15.

  Next, the operation of the multi-cathode sputtering film forming apparatus will be described. First, a process gas, usually Ar, is supplied into the reaction vessel 10 through the gas inlet 16. The pressure inside the reaction vessel 10 is maintained higher than 5 Pa (Pascal). In the reaction vessel 10, a plasma is generated by applying an rf current to one selected cathode or several selected cathodes. The rf current is usually applied to the selected cathode that needs to be sputtered. Thus, if two different materials need to be sputtered simultaneously, rf current is applied to both cathodes simultaneously.

When the plasma is generated by capacitive coupling of rf power, a negative self-bias voltage is generated on the selected cathode. Depending on the applied rf power, the frequency of the rf current and the value of the pressure self-bias voltage vary. This negative self-bias voltage creates a DC electric field on the surface of the cathode (11a-11d), which accelerates ions in the plasma, such as Ar ⁺ ions. The collision of high energy ions at the cathode surface causes the cathode material to be sputtered and bring the spatter into the plasma.

Sputtered atoms emitted from the cathode are in a neutral state. Due to the higher pressures employed, these sputtered atoms will experience a great deal of collisions before depositing on the wafer 24 or other surfaces inside the reaction vessel 10. Collisions with Ar ⁺ ions and Ar ^* excited states result in ionization of sputtered atoms. Accordingly, some of the sputtered atoms are ionized in the gas phase. The ionized portion of the sputtered atoms depends on the distance between the cathode (11a-11d) and the wafer 24, the pressure, and the plasma density in the reaction vessel 10.

  If rf current is applied to the lower electrode 15, a negative self-bias voltage is generated on the surface of the wafer 24. This negative self-bias voltage generates a DC electric field that accelerates ionized sputtered atoms to the surface of the wafer.

  If the bottom electrode 15 is not supplied with rf current and is also not connected to ground, the wafer 24 is in an electrically floating state. In this state, the wafer voltage is given as a floating voltage (Vf). This floating voltage (Vf) is always lower than the plasma voltage (Vp). Therefore, there is a voltage difference (electric field) defined by Vp−Vf. This voltage difference generates an electric field toward the wafer 24. This electric field accelerates ionized sputtered atoms in the plasma toward the surface of the wafer. Therefore, most of the ionized sputtered atoms reach the wafer surface perpendicularly.

  The phenomenon described above is schematically shown in FIG. In FIG. 3, the dotted line 25 near the surface of the wafer 24 shows the radial profile of the atom or ion flow (flux) from the cathode 11a and the region 26 shows the plasma. Further, the electric field (E) is generated toward the surface of the wafer 24 as indicated by an arrow based on the voltage difference (Vp−Vf). In the plasma 26, the sputtered atoms emitted from the cathode 11 a move as indicated by the passage 27. Sputtered atoms ionized according to the movement path 27 of the sputtered atoms are accelerated to the wafer surface and almost reach the wafer surface perpendicularly. This action thus results in uniform sidewall coverage and better bottom coverage in the holes and grooves 29 in the wafer 24 as shown in FIG.

  However, the flow of ionized or neutral atoms is not uniform on the wafer surface. It is a highly asymmetric pattern as shown by line 25 in FIG. Line 15 represents the density of the flow of atoms or ionized atoms with respect to the cathode 11a. However, since the wafer 24 is rotated about its central axis 24a as shown in FIG. 1, the resulting film exhibits good uniformity.

  Next, instead of the above-described rf generator 19, a DC power source for supplying a DC voltage to the cathodes 11a to 11d can be used. The purpose of applying a DC voltage to the cathode is to increase the sputtering rate of the cathode or target by increasing the negative voltage of the cathode. In addition, the use of an rf generator or a DC power source may be determined depending on the cathode material.

  According to the first embodiment, the effect is to provide better sidewall and bottom coverage in the holes or grooves in the wafer surface.

[Embodiment 2]
A second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, FIGS. 5 and 6 correspond to FIGS. 1 and 2, respectively. Compared with the multi-cathode sputtering film forming apparatus of the first embodiment, the apparatus of the second embodiment has a central cathode 11e parallel to the lower electrode 15 added. The center electrode 11e has substantially the same structure as the inclined cathodes 11a to 11d described above, and has the same function. The diameter or size of the central cathode need not be the same as that of the tilted cathode. All the other hardware is the same as described in the first embodiment, except for the above addition regarding the central cathode and the related configuration. Therefore, in FIGS. 5 and 6, substantially the same elements as those described in the first embodiment are denoted by the same reference numerals. The method of operation and the advantages obtained in the second embodiment are likewise the same as described in the first embodiment.

[Embodiment 3]
A third embodiment of the present invention will be described with reference to FIG. FIG. 7 corresponds to FIG. 5 of the second embodiment. The only difference here is that the cathodes 11a to 11e are connected to the DC power supply unit 31 in addition to the rf power supply unit, as compared with the second embodiment. Therefore, during operation, one or all cathodes are provided with DC power in addition to rf power. Application of additional DC power to the cathode results in an increase in its negative voltage. This increases the sputtering rate of the cathodes 11a-11e. Except for adding the DC power supply 31 as described above, all the hardware is the same as that described in the first or second embodiment. Therefore, in FIG. 7, the same reference number is attached | subjected to the element substantially the same as the element demonstrated in 1st or 2nd embodiment. The resulting method of operation and advantages are likewise the same as those described in the first or second embodiment.

  The present invention uses a sputtered neutral atom in each of the tilted multi-cathodes in a PVD sputtering apparatus to form better coverage of patterned deep hole or trench sidewalls and bottoms at the wafer surface. Used for

This figure is a longitudinal sectional view of the apparatus according to the first embodiment of the present invention. This figure is a bottom view showing the cathode arrangement in the reaction vessel shown in FIG. This figure is an explanatory diagram showing the path of sputtered atoms from the cathode to the wafer surface. This figure is a longitudinal section showing the coverage of the hypothetical side and bottom of a hole or groove on the wafer surface. This figure is a longitudinal sectional view of an apparatus according to the second embodiment of the present invention. This figure is a bottom view of the cathode arrangement in the reaction vessel shown in FIG. This figure is a longitudinal sectional view of an apparatus according to a third embodiment of the present invention. This figure is a longitudinal sectional view of a conventional apparatus. This figure is a bottom view of the cathode arrangement in the reaction vessel shown in FIG. This figure is an explanatory diagram showing the direction of the flow of sputtered atoms. This figure is a longitudinal sectional view of a hole or groove after thin film formation using the reaction vessel shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Reaction container 11a-11e Cathode 12 Wafer holder 15 Lower electrode 18 Magnet 19 rf generator

Claims (3)

Controlling the reaction vessel pressure to a pressure higher than 5 Pa,
Placing the wafer in a wafer holder in the reaction vessel and rotating the wafer;
With respect to the wafer, it is arranged to tilt the motor Getto and cathode,
Applying an rf current to the cathode from an rf generator ;
Ionizing sputtered atoms emitted from the cathode , generating plasma in the reaction vessel , and
Making the lower electrode provided in the wafer holder non-grounded , non-RF connected, and non-DC connected so that the wafer is floating in potential.
When the plasma is generated by capacitive coupling of the rf power of the rf generator, a negative self-bias voltage is generated on the selected cathode to ionize sputtered atoms emitted from the cathode and negative bias Depositing a film on the inner surface of a hole or groove made in the wafer surface, so as to be accelerated by an electric potential ;
A sputtering method characterized by the above. The cathode, in addition to the rf current sputtering method according to claim 1, characterized in that the DC current is further supplied. The target is formed by High-k dielectric material, the High-k dielectric material, a sputtering method according to claim 1 or 2, characterized in that a HfSiON.

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